The invention relates to a capacitive sensor array having a sensor electrode which enables the detection of the intrusion of an object into a space in front of the sensor electrode, and a control and evaluation circuit coupled with the sensor electrode that detects a change in the capacitance of the sensor electrode compared to a reference potential by periodically and repeatedly coupling the sensor electrode, at a predetermined frequency, with a predetermined first potential and evaluating at least one parameter of a current or voltage profile dependent on the periodic charging and discharging of the sensor electrode for detecting the capacitance change.
A capacitive sensor array of the type named in the introduction in which the reference potential is a ground potential and the first potential is an operational voltage potential and in which the parameter of a current or voltage profile dependent on the periodic charging and discharging of the sensor electrode is a voltage that can be measured over a capacitor, which voltage depends on the charge accumulated on the capacitor, wherein this charge is accumulated by charging the sensor electrode by periodically and repeatedly coupling it with a power supply potential and then discharging it by coupling it with the capacitor, is known, for example, from the U.S. Pat. No. 5,730,165 or the corresponding patent DE 196 81 725 B4. Another such capacitive sensor is known from the patent EP 1 339 025 B1.
A capacitive sensor array having a sensor electrode, with a ground-background electrode arranged at a distance behind the sensor electrode and with a shield electrode which is arranged between the sensor electrode and the ground-background electrode and is connected via a control and evaluation circuit coupled in such a manner with the sensor electrode that it has no influence on the capacitance of the sensor electrode measured against the ground and that its potential is adjusted to the potential of the sensor electrode is known, for example, from the publications EP 0 518 836 A1, U.S. Pat. No. 6,825,752 B2, DE 101 31 243 C1 and DE 10 2006 044 778 A1. This provision of a shield electrode between the sensor electrode and the background electrode located on ground potential which is known from these documents has the advantage that the sensitivity of the thus formed capacitive sensor to changes in the area in front of the sensor electrode is increased, for example, by the insertion of objects. This is mainly due to the fact that the field extending out from the sensor electrode extends more in the space in front of the sensor electrode because a large part of the field is no longer short-circuited to the background electrode located on the ground potential, as it is when there is no shield electrode. Due to the fact that the shield electrode is coupled with the sensor electrode in such a way that its potential is adjusted, a strong electric field builds up between the shield electrode and the background electrode; above all, however, there is virtually no build-up of a field between the sensor electrode and the shield electrode adjusted according to potential.